add dedicate sync object and user assertions in place of exceptions

Author: Wraith2

src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/SqlClient/SNI/SNIMarsConnection.cs

@@ -14,6 +14,7 @@ namespace Microsoft.Data.SqlClient.SNI
     /// </summary>
     internal class SNIMarsConnection
     {
+        private readonly object _sync;
         private readonly Guid _connectionId;
         private readonly Dictionary<int, SNIMarsHandle> _sessions;
         private SNIHandle _lowerHandle;
@@ -26,14 +27,15 @@ internal class SNIMarsConnection
 
         public int ProtocolVersion => _lowerHandle.ProtocolVersion;
 
-        public object DemuxerSync => this;
+        public object DemuxerSync => _sync;
 
         /// <summary>
         /// Constructor
         /// </summary>
         /// <param name="lowerHandle">Lower handle</param>
         public SNIMarsConnection(SNIHandle lowerHandle)
         {
+            _sync = new object();
             _connectionId = Guid.NewGuid();
             _sessions = new Dictionary<int, SNIMarsHandle>();
             _demuxState = DemuxState.Header;

src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/SqlClient/SNI/SNIMarsHandle.cs

@@ -56,10 +56,7 @@ internal sealed class SNIMarsHandle : SNIHandle
         public override void Dispose()
         {
             // SendControlPacket will lock so make sure that it cannot deadlock by failing to enter the DemuxerLock
-            if (_connection != null && Monitor.IsEntered(_connection.DemuxerSync))
-            {
-                throw new InvalidOperationException("SNIMarsHandle.HandleRecieveComplete should be be called while holding the SNIMarsConnection.DemuxerSync because it can cause deadlocks");
-            }
+            Debug.Assert(_connection != null && Monitor.IsEntered(_connection.DemuxerSync), "SNIMarsHandle.HandleRecieveComplete should be be called while holding the SNIMarsConnection.DemuxerSync because it can cause deadlocks");
             long scopeID = SqlClientEventSource.Log.TrySNIScopeEnterEvent(s_className);
             try
             {
@@ -301,10 +298,7 @@ private uint SendPendingPackets()
         /// <returns>SNI error code</returns>
         public override uint SendAsync(SNIPacket packet, SNIAsyncCallback callback = null)
         {
-            if (Monitor.IsEntered(_connection.DemuxerSync))
-            {
-                throw new InvalidOperationException("SNIMarsHandle.HandleRecieveComplete should be be called while holding the SNIMarsConnection.DemuxerSync because it can cause deadlocks");
-            }
+            Debug.Assert(_connection != null && Monitor.IsEntered(_connection.DemuxerSync), "SNIMarsHandle.HandleRecieveComplete should be be called while holding the SNIMarsConnection.DemuxerSync because it can cause deadlocks");
             long scopeID = SqlClientEventSource.Log.TrySNIScopeEnterEvent(s_className);
             try
             {
@@ -438,10 +432,7 @@ public void HandleSendComplete(SNIPacket packet, uint sniErrorCode)
         /// <param name="highwater">Send highwater mark</param>
         public void HandleAck(uint highwater)
         {
-            if (Monitor.IsEntered(_connection.DemuxerSync))
-            {
-                throw new InvalidOperationException("SNIMarsHandle.HandleRecieveComplete should be be called while holding the SNIMarsConnection.DemuxerSync because it can cause deadlocks");
-            }
+            Debug.Assert(_connection != null && Monitor.IsEntered(_connection.DemuxerSync), "SNIMarsHandle.HandleRecieveComplete should be be called while holding the SNIMarsConnection.DemuxerSync because it can cause deadlocks");
             long scopeID = SqlClientEventSource.Log.TrySNIScopeEnterEvent(s_className);
             try
             {
@@ -468,10 +459,7 @@ public void HandleAck(uint highwater)
         /// <param name="header">SMUX header</param>
         public void HandleReceiveComplete(SNIPacket packet, SNISMUXHeader header)
         {
-            if (Monitor.IsEntered(_connection.DemuxerSync))
-            {
-                throw new InvalidOperationException("SNIMarsHandle.HandleRecieveComplete should be be called while holding the SNIMarsConnection.DemuxerSync because it can cause deadlocks");
-            }
+            Debug.Assert(_connection != null && Monitor.IsEntered(_connection.DemuxerSync), "SNIMarsHandle.HandleRecieveComplete should be be called while holding the SNIMarsConnection.DemuxerSync because it can cause deadlocks");
             long scopeID = SqlClientEventSource.Log.TrySNIScopeEnterEvent(s_className);
             try
             {